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Appendix VI.

or, indeed, to any other process where a sudden supply of intense
heat is desired.

i                              We may now explain the actual apparatus adopted in the

!                         welding of trarn rails; and, firstly, it must be understood that not

i                         only are the rails welded, but a portion of iron (from the thermit)

is run all round the joint, for which a mould is to be provided.

The pattern for the half-mould is shewn at A, Fig. 947, consisting

of a copy of the halfrail, the scum head, and the wrapping of

molten iron.    A box B is fitted o\rer this, as seen dotted, and a

mixture of sand and clay is rammed between the box and the

pattern to the appearance shewn at c.   Two of these moulds

having been made, and dried in a portable oven at 600 F. for

)                         two hours, the rail D is painted on the tread and sides of the head

 so as to prevent adherence of metal at these places; and the

moulds with their cases are placed one on each side of the rail,

and clamped together as at E.   The rails having been previously

secured end to end by the clamps F F and the connecting bolts G,

the mould and rail are now well luted with sand and clay round

all the meeting edges, especially at the head.    The crucible H,

! 1                         lined with magnesia, is supported with its mouth about 3 or 4

i ;'                        inches above the mould, and the opening is closed by two thin

i                         asbestos washers and an iron disc, held up by a \ in, iron rod j

and the spade K.   The washers are covered with magnesia to

prevent accidental tapping.   The crucible is next filled with the

;'                        thermit   mixture, poured from a bag,  and a salt-spoonful of

ignition powder is placed upon the top.    Protecting his eyes with

1 '                         blue spectacles, the workman starts the ignition by means of a

s                        lucifer match, covering the crucible, and the combustion is com-

\                           pleted in about to seconds.    He then deftly withdraws the spade

','                        after lifting the tapping rod, and the molten mixture runs into the

rail mould, firstly the iron, on account of its greater weight, and

' ;                        afterwards the slag, which has equal weight with the iron but

 i(                        three times its volume.   Finally, after 3 minutes' wait for the

uniform welding heat, the bolts o G- are tightened up to cause a

true weld between the rail ends; and, after another short rest to

!|                         cool, the mould and superfluous material are broken away with a

j|                         sledge-harnrner^ the whole process having occupied 30  or 40

;|                         minutes.    The action of the tightening bolts G has caused some